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Introduction: Platelet-rich plasma (PRP) therapy is used to treat pathological conditions such as degenerative inflammatory diseases including osteoarthritis (OA) by enhancing tissue repair and promoting anti-inflammatory effects. Although PRP therapy for patients with knee OA improved pain and functional scores, the association of clinical outcomes and quality of PRP including cell composition and concentration is unclear. Methods: Therefore, this study analyzed blood cell counts, including the immature platelet fraction (IPF), in peripheral blood and PRP of 144 patients with knee OA who underwent PRP therapy. The mean leukocyte and platelet concentrations in whole blood and PRP were analyzed using an XN-1000 automated hematology analyzer. Visual analogue scale (VAS) scores and knee injury and osteoarthritis outcome scores (KOOS) before and 1 month after a single PRP injection were also determined. Results: Higher platelet and lower leukocyte concentration rates were observed in PRP compared with whole blood. The platelet concentration in whole blood was negatively correlated with VAS improvement. The percentage of IPF (IPF%) in whole blood was positively correlated with VAS improvement and KOOS (pain) improvement, whereas the IPF% in PRP tended to correlate with VAS improvement. Furthermore, multivariate logistic regression demonstrated the high IPF% in whole blood was significantly associated with VAS improvement. The low percentage of neutrophil (neutrophil%) in PRP was significantly associated with the VAS improvement and KOOS (ADL) improvement. Conclusions: Therefore, PRP efficacy for OA might depend on the patient's biological status.

Introduction: Researchers have investigated the use of platelet-rich plasma (PRP) therapy. However, the mechanisms through which PRP affects tissue repair remain unclear. We hypothesize that PRP promotes tissue repair through not only via direct manner on the local cells but also via indirect manner that encourage the recruitment of reparative cells such as macrophages (MPs), and it depends on the quality of PRP including the concentration of leukocytes. The aim of this study is to elucidate the actions of the MPs in the mechanisms of PRP on tissue repair processes. Methods: Leukocyte-rich (LR) PRP and leukocyte-poor (LP) PRP were prepared from 12-week-old C57BL6 mice. Full-thickness defects were created in central third of patellar tendons of 12-week-old C57BL/6 mice for histologic analysis (n = 36) and 12-week-old B6.129P-Cx3cr1tm1Litt/J mice for flow cytometry analysis (n = 108). B6.129P-Cx3cr1tm1Litt/J mouse is GFP-positive only in the MP-linage cells thus MPs recruited to the repair tissue can be distinguished whether it had originated from administrated PRP or recruited from host mouse. Mice were treated either with LR-PRP, LP-PRP, or without PRP (control group). Histological analyses were performed to evaluate the tendon healing using Bonar score as semi-quantitative histological scoring system. Flow cytometric analyses were performed to count the number of GFP-positive cells around repaired patellar tendon. In addition, the ratio of pro-inflammatory MPs (M1)/anti-inflammatory MPs (M2) were analyzed in those GFP-positive cells. The statistical analysis was performed using GraphPad Prism ver6. P values